Field of the Invention
The invention relates to a method for controlling an occupant protection device in a vehicle.
In a known method for controlling an occupant protection device in a vehicle, a crash sensor supplies a crash signal. A crash variable derived from the crash signal is thereupon compared with a threshold. The occupant protection device is controlled as a function of an overshooting of the threshold by the crash variable. As a rule, in this case the threshold contains at least one term that is determined from the crash signal.
In this case, the threshold usually contains a plurality of terms that are additively combined with one another, each term per se, that is to say without taking account of the prescribed sign, being considered with positive values in the threshold. In International Patent Disclosure WO 94/14638, the threshold is composed, for example, of a constant term with the inclusion of a term for the average acceleration and excluding a so-called dynamic term which takes account of a maxima and a minima in the acceleration signal. According to the prior art, therefore, each threshold value term initially supplies a positive contribution. The constants, and also the term of the average acceleration, feature with a positive sign in the threshold value, and so their contributions can contribute only to increasing the threshold in a marked or less marked form. The so-called dynamic term, by contrast, features in the threshold value calculation with a prescribed negative sign, such that the term, which of itself supplies positive values, supplies values which lower the threshold because of the prescribed sign. The prescribed combination of the individual terms can therefore certainly lead to a rise or fall in the threshold. However, viewed per se, each term can supply exclusively positive contributions.
It is accordingly an object of the invention to provide a method for controlling an occupant protection device in a vehicle, and a control device therefor which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, in which a threshold reacts extremely flexibly to the crash signal characterizing the course of the accident.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling an occupant protection device in a vehicle. The method includes using a crash sensor for supplying a crash signal, deriving a crash variable from the crash signal, and comparing the crash variable with a threshold. The threshold includes at least one term determined by the crash signal or a derived signal derived from the crash signal. The term is configured such that, depending on a configuration of the crash signal, it supplies one of a first contribution which raises the threshold and a second contribution which lowers the threshold. The term is determined by positive and negative components summed separately from one another of the crash signal or the derived signal. The occupant protection device is controlled in dependence on an overshooting of the threshold by the crash variable.
In the invention, the sensor detecting the accident or crash supplies the crash signal. The sensor can be configured as an acceleration sensor that supplies an acceleration signal. In this case, the axis of sensitivity of the acceleration sensor is preferably aligned in that direction from which it is intended to detect a crash. Acceleration sensors for detecting crashes from the side are therefore preferably sensitive transverse to the vehicle longitudinal axis and are fastened in the center of the vehicle, but also on the side of the vehicle on side doors or door sills. An acceleration sensor for detecting a front crash is preferably likewise disposed in the center of the vehicle, but possibly also on the front of the vehicle, and picks up acceleration signals along the vehicle longitudinal axis. However, it is also possible to provide as crash sensors sensors for the direct or indirect penetration of an obstacle into the vehicle. For example, in a direct type a capacitively configured deformation sensor picks up the penetration of an obstacle, in the case of this sensor the outer skin of the vehicle being provided as an electrode, and a further electrode being provided which cooperates with the vehicle outer skin and is installed in a stationary fashion. In an indirect way, a crash sensor can preferably detect a crash from the side by picking up an air pressure in a cavity in the vehicle door. The deformation of the vehicle door initiated by the penetration of the obstacle varies the volume of the cavity, and this leads to a rise in air pressure that can be detected in the crash signal, which is configured as a pressure signal. A crash variable that is compared with a threshold is usually derived from such a crash signal. The crash variable can in this case be the crash signal itself, or preferably be derived from the crash signal by mathematical calculations. In this case, it is preferable to use a partial speed loss, also termed delta V, as the crash variable. For this purpose, the acceleration signal, which is subsequently used as the crash signal, is integrated from the start of the crash. The integrated acceleration signal therefore supplies the decrease in speed from the start of the crash. A partial speed loss is then formed by the difference between the actual speed value and a speed value that was and is stored in a memory determined at an earlier instant. The partial speed loss is preferably compared with the threshold.
The threshold is of variably configured, in this case, and can assume different threshold values over time. The threshold is usually composed additively in this case from a plurality of terms. Each term is a mathematical expression of self-contained content. One term of the threshold can be a constant in this case. Another term can have, for example, a time-linear member in this case. The threshold preferably therefore contains a plurality of terms that are related to one another additively.
The threshold in this case contains at least one term that is determined by the crash signal. Determination by the crash signal can be provided in various ways. Thus, for example, a term can contain the crash signal or a signal derived from the crash signal and directly proportional thereto. As a result, the threshold value characteristic is proportional to the crash signal at least in this term. In a further version, such a term can be determined by the crash signal with the aid of logic combinations. Thus, the term can provide a first constant value when the crash signal undershoots an assigned value. A second, higher constant value can be provided as soon as the crash signal overshoots the assigned value.
The occupant protection device is controlled as a function of the overshooting of the threshold by the crash variable. The occupant protection device can be triggered directly in this case when the threshold is overshot by the crash variable. The overshooting of the threshold by the crash variable can alternatively, however, be one of a plurality of triggering criteria which are logically combined with one another and, in particular, combined with one another in a Boolean fashion. The overshooting of the threshold cooperating only, for example, with the fulfillment of a further criterion for the purpose of activating the assigned occupant protection device. Airbags, in particular driver, passenger, side, head, chest or other airbags, can be provided as the occupant protection device, as can also seat belt pretensioners or rollover protection devices.
According to the invention, at least one term of the threshold is configured in such a way that, depending on the configuration of the crash signal, it supplies a contribution that raises the threshold or a contribution that lowers the threshold. Accordingly, the term itself can supply both positive and negative values as a function of the crash signal. If, therefore, such a term is introduced into the threshold with a positive sign fixed a priori, the term can raise the threshold or lower it, an overall raising of the threshold or an overall lowering of it also depending, of course, on the contributions of further terms. If such a term with a negative sign fixed a priori is introduced into the threshold, in the event of the supply of negative contributions the term can raise the threshold, and in the event of the supply of positive contributions it can lower the threshold. It is fundamental to the invention that, therefore, a singular term is configured in such a way that it can react in an extremely flexible and rapid way to the crash signal as a function thereof and, consequently, can not only raise the threshold to a lesser or greater extent, but can also simultaneously lower the threshold when it appears from the crash signal that lowering of the threshold is indicated.
The term can be determined from the start of the crash by a speed loss of the vehicle derived from the crash signal. In this case, the speed loss is usually determined by integrating the acceleration from the start of the crash, which is to say from the overshooting of an initial limiting value by the acceleration picked up. The speed loss thereby reproduces the overall energy loss during the crash. The speed loss is determined during the period of the overall crash and at any time supplies the information on the crash energy reduced from the start of the crash up to the respective instant. Consideration of the energy of the crash is therefore imported into the threshold value characteristic with the aid of this term, such that the occupant protection device is triggered as a function of the reduced kinetic energy, and thus as a function of the severity of the crash.
A further term of the threshold is directed toward detecting oscillations in the crash signal. Strong oscillations in the crash signal usually permit the inference of a crash in which the occupant protection device is not to be triggered. Such so-called misuse impacts are, for example, introduced by a hammer blow against the vehicle body. Such a hammer blow can lead to large deceleration amplitudes on the vehicle. However, the vehicle can reduce the transmitted energy by vibrating strongly. Whereas in the event of a severe crash in which the occupant protection device is to be triggered, a larger impulse usually acts on the vehicle such that it is not possible for the vehicle to reduce the transmitted energy through dissipation by vibration. Thus, taking account of the oscillations in the crash signal preferably serves to distinguish misuse crashes from severe accidents.
Another term likewise serves to distinguish a misuse crash from a xe2x80x9cnormalxe2x80x9d crash. Once again, a strong tendency to oscillation in the crash signal is characteristic of a misuse crash, the crash signal oscillating about the zero point, in particular. Energy transmitted by a short impact (misuse) can be reduced by oscillation of the vehicle. By contrast, in the event of a normal crash the crash signal predominantly exhibits values in a direction of deceleration. By considering the instants at which the crash signal overshoots an upper threshold value and, on the other hand, undershoots a lower threshold value, it is possible to influence the threshold in an advantageous way. If the crash signal undershoots the lower threshold value, and if the threshold value is in a range of values in which a crash signal resulting from a normal crash is expectedxe2x80x94in the event of an impact a deceleration, that is to say a negative acceleration, is expected as a rulexe2x80x94the absolute value of the threshold is lowered successively by increments during the time interval in which the crash signal exceeds the upper limiting value, and triggering is facilitated. If, however, the crash signal overshoots an upper limiting value which preferably has a sign opposite to the lower limiting value, and thereby characterizes acceleration values opposing the direction of the crash, successive incremental values are added in absolute terms to the threshold during this time interval, and triggering is thereby rendered more difficult.
Still another term is described which likewise features in the threshold value calculation in addition to the other, previously described terms, preferably in an additive fashion. Acceleration pulses in the crash signal that are significant in the event of a crash owing to the penetration of an obstacle are detected with the aid of a term of such configuration as an indicator for mechanical deformation of the vehicle body structure, and the threshold is influenced in accordance therewith.
In accordance with an added mode of the invention, there is the step of determining the term from a speed loss of the vehicle from a start of a crash determined from the crash signal.
In accordance with an additional mode of the invention, there is the step of determining a ratio of a negative component to a positive component, and the term is determined by a difference between the ratio and a limiting value.
In accordance with another mode of the invention, there is the step of providing the difference with different weighting factors in the term, depending on whether the ratio overshoots or undershoots the limiting value.
In accordance with a further mode of the invention, there is the step of determining the term by an overshooting of an upper limiting value by the crash signal or the derived signal and also by an undershooting of a lower limiting value by the crash signal or the derived signal. The term supplies a contribution that raises an absolute value of the threshold when the upper limiting value is overshot, and the term supplies a contribution which lowers the absolute value of the threshold when the lower limiting value.
In accordance with another added mode of the invention, there is the step of determining the threshold by a difference in levels of two time-sequential extreme values in one of the crash signal and the derived signal.
In accordance with another additional mode of the invention, there is the step of lowering the threshold in absolute value in dependence on a difference in the levels of the two time-sequential extreme values.
In accordance with a concomitant mode of the invention, there is the step using an acceleration sensor for supplying the crash signal and the crash signal is determined by a current vehicle acceleration.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a control device for an occupant protection device. The control device includes a microprocessor programmed to perform the steps described above.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for controlling an occupant protection device in a vehicle, and a control device therefor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.